In a conventional radar apparatus, in a case where an object having large reflection exists farther than a distance equivalent to a transmission repetition cycle, what is called a multi-order echo mixes into a reception signal, to cause erroneous detection.
As a technology to prevent influence by such a multi-order echo, in a technology disclosed in Patent Document 1, multi-order echo clutter is specified and deleted based on a difference between reception signals by transmission pulse cycles of a short distance range and a long distance range.
Further, in a technology disclosed in Patent Document 2, by using a transmission frequency signal which is set to a frequency which increases or decreases by a predetermined frequency every pulse repetition cycle, a primary echo and a multi-order echo can be discriminated based on a speed.
Further, in a technology disclosed in Patent Document 3, interference is avoided by arbitrarily selecting a plurality of transmission stagger-trigger generation circuits.
Further, in a radar apparatus, it is necessary to avoid interference between a reflection wave being a wave radiated by itself and reflected by a target object and a radio wave radiated from another radar apparatus, but avoiding the interference is not easy in a case where, in particular, the radar apparatus itself and another radar apparatus which becomes an interference source are similar radar apparatuses.
As a means to avoid such mutual interference, regarding a FMCW (Frequency Modulated Continuous Wave) radar, there is known a method to prevent interference by controlling a cycle, a transmission interval, or a modulation gradient of a FMCW modulation signal.
Further, regarding a pulse radar, there are known a method, as described in Patent Document 4, to prevent interference by controlling a turning direction of a circular polarized wave, a method, as described in Patent Document 5, in which transmission is halted, only a reception circuit is operated to receive a radio wave, a received signal is stored in a storage unit as an unnecessary signal, and thereafter, normal measurement is carried out and the unnecessary signal is removed therefrom, and so on.
Further, as a technology to remove clutter in a pulse radar, in general, there are known a method, as described in Patent Document 6, in which, regarding a composite pulse radar transmitting a plurality of transmission pulses during one cycle of transmission reception repetition cycles, a time interval between the transmission pulses is varied every transmission reception repetition cycle, that is, a pulse repetition frequency (PRF) is varied and in a case where a series of target reflection reception signals are observed with a timing of any transmission pulse among the transmission pulses being a criteria, the target reflection reception signals appearing at a different time position every repetition time period are removed by an asynchronous signal removal processing circuit, and so on.